\(B=\dfrac{1}{4}\times\left(\dfrac{4}{1\times5}+\dfrac{4}{5\times9}+\dfrac{4}{9\times13}+...+\dfrac{4}{125\times129}\right)\)
\(=\dfrac{1}{4}\times\left(1-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+...+\dfrac{1}{125}-\dfrac{1}{129}\right)\)
\(=\dfrac{1}{4}\times\left(1-\dfrac{1}{129}\right)=\dfrac{1}{4}\times\dfrac{128}{129}=\dfrac{32}{129}\)
\(\dfrac{1}{1x5}\)+\(\dfrac{1}{5x9}\)+\(\dfrac{1}{9x13}\)+....+\(\dfrac{1}{45x49}\)
Tính nha
Tìm x
1/1x5 + 1/5x9 + 1/9x13 +....+1/77x81 + 1/x(x+4)= 29/117
Tính nhanh
a, 4/1x5 + 4/5x9 + 4/9x13 + ... + 4/91 x 95 + 4/95 x 99
b, 1/6 + 1/12 + 1/20 + ... + 1/132
Tính:
(2007 - 2005) + (2003 - 2001) +...+ (7 - 5) + (3 - 1)
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Viết tiếp 3 số hạng thứ 8;9 và 10 của dãy số sau: \(\dfrac{1}{1x5};\dfrac{1}{5x9};\dfrac{1}{9x13};...\)
Tính 3/1x5+3/5x9+3/9x13+3/13x17+3/17x21
Tìm X:
4xX/1x5+4xX/5x9+4xX/9x13+4xX/13x17=16
I=\(\dfrac{2}{1x5}\)+\(\dfrac{2}{5x9}\)+\(\dfrac{2}{9x13}\)+.....+\(\dfrac{2}{181x185}\)
7/1x5 + 7/5x9 + 7/9x13 + 7/13x17 + 7/17x21
Hướng dẫn giúp m
4/1x5 + 4/5x9 + 4/9x13 +.......+ 4/(X-4)x(X) = 15/17
